This invention relates to a sheet separating apparatus for removing sheets one by one from a stack of sheets.
The invention has application, for example, to a currency note picking apparatus for extracting notes from a currency cassette used in an automated teller machine (ATM). As is well known, in operation of an ATM a user inserts a customer identifying card into the machine and then enters certain data (such as codes, quantity of currency required or to be paid in, type of transaction, etc.) upon one or more keyboards associated with the machine. The machine then processes the transaction, updates the user's account to reflect the current transaction, dispenses cash when requested, (extracted from one or more currency cassettes mounted in the machine), and returns the card to the user as part of a routine operation.
One known kind of sheet separating apparatus is represented by a currency note picking mechanism which incorporates pivotably mounted vacuum operated pick arms disposed adjacent an associated currency cassette. The pick arms are arranged to draw part of an end note of a stack of notes in the cassette away from the remainder of the stack by applying suction force to the end note, and to position said part for engagement by transport means arranged to remove the end note from the cassette. The pick arms are pneumatically connected to a piston operated vacuum pump via mechanical timing means. Because the reduced pressure generated by the piston operated pump varies in a periodic manner, precise mechanical timing is required to ensure that a maximum suction force is applied by the pick arms when needed. Some problems have been experienced with this known apparatus in that timing drift may occur due to component manufacturing variations and wear, resulting in possible failure to pick a currency note.
U.K. Patent Application 2085411 A discloses a currency note picking apparatus including pivotably mounted suction heads pneumatically connected via a mechanical timing valve to a vane pump which in operation continuously generates a reduced pressure. The timing valve is mounted to operate in synchronism with the swinging movement of the suction heads and is arranged to control the time at which reduced pressure is applied to the suction heads. Although this apparatus avoids problems due to periodically varying reduced pressure, it has the disadvantages that the mechanical valve requires precise construction, and that the timing of the operation of the mechanical valve is not readily adjustable so that problems are likely to be experienced in maintaining reliable operation in the face of changing operational requirements.